The major urinary metabolite of the pineal hormone metatonin, 6-hydroxymelatonin is being quantified by gas chromatography-negative chemical ionization mass spectrometry. Urinary excretion rates of this metabolite are being used to determine the possible role of the pineal gland in human reproductive biology - i.e., its function during pubertal development and throughout the menstrual cycle. A longitudinal study of melatonin metabolite excretion by young girls is in the third year. Each girl has maintained a self-consistent level of excretion, which has not, as yet, correlated with pubertal change. In a study of six menstruating adult women, daily variations in melatonin metabolite exretion were measured for two menstrual cycles. There were no consistent changes with regard to key normal events in each cycle. Day-to-day variations were more significant than those observed in pre-pubertal girls, suggesting either a day-to-day change in pineal function or another unanticipated study variable. A correlative study of plasma radioimmunoassayable melatonin vs. urinary 6-hydroxymelatonin is in progress to resolve this issue. An assay of urinary 5-methoxyindoleacetic acid, a candidate melatonin metabolite, has been developed and applied to human and candidate melatonin metabolite, has been developed and applied to human and animal samples. It does not reflect pineal gland activity in man or rat.